Typically, injections are performed with syringes that pierce the skin with a needle to deliver medication to a desired location on a body. In a large number of cases the syringes are pre-filled with a medication. However, if the medication does not have a long shelf life, it must be mixed just prior to an injection to maintain potency. This requires the medication to be mixed externally to the syringe and then drawn in using needles or the like. After drawing in the medication, the injection is administered in a normal manner. But, after the injection there are one or more needles that need to be disposed of, increasing costs and increasing the potential health hazards from exposure to used needles.
As an alternative to needle delivery injections, needle-less medication injections have been performed with "permanent gun" instruments, generally referred to as "jet injectors". These devices use either a compression spring or a compressed inert gas to propel the fluid medication (via a push rod plunger) through a small orifice (an injector nozzle) which rests perpendicular to and against the injection site. The fluid medication is generally accelerated at a high rate to a speed of between about 800 feet per second (fps) and 1,200 fps (approximately 244 and 366 meters per second, respectively). This causes the fluid to pierce through the skin surface without the use of a needle, resulting in the medication being deposited in a flower pattern under the skin surface. These reusable jet injectors can accept pre-loaded medication cartridges, but again the cartridges must be pre-loaded just prior to an injection for certain medications with short shelf lives. The procedure is to again use a needle and a syringe to mix and then load the medication in the cartridge prior to an injection. After drawing in the medication, the needle-less injection is administered in a normal manner. But, after the injection there are again one or more needles that need to be disposed of, increasing costs and increasing the potential health hazards from exposure to used needles.
Single use needle-less jet injectors offer an alternative to multi-use, needle-less injectors, since they are low cost and can be pre-loaded at the point of manufacture. However, if the medication does not have a long shelf life, the pre-loading is impractical. Thus, single-use, needle-less injectors have not been usable with medications that must be mixed prior to injection. An alternative to overcome this drawback was to include a two compartment ampule in the injector, which is opened up with a piercing mechanism and combined together to mix the medication as the injection takes place. Although, this obviates the need for needles, the results are unsatisfactory, since the medication is not always thoroughly mixed and properly deposited under the skin. In addition, improper mixing can allow the medication (particularly large molecule medications) to be destroyed or altered during the injection process. Further, it is possible for the piercing mechanism included in the ampule to break the barrier between diluent and reagent may block or obscure the orifice, or jam the needle-less injector leading to an improper injection.